1. Field of the Invention
The present invention relates to a superconducting wire exhibiting a stable characteristic even when an external pressure such as a load is applied, and a method of manufacturing the same.
2. Description of the Related Art
For example, it is known that, in a superconducting wire of a metal compound superconductor such as Nb.sub.3 Sn, its superconducting characteristic is degraded when a tensile stress in the longitudinal direction or a compressive stress (a load in a direction perpendicular to the longitudinal direction, or a lateral compressive stress) within a section is applied. In particular, regarding the lateral compressive stress, the superconducting characteristic, e.g., a critical current density, is easily degraded when a stress of as small as about 1/10 the tensile stress in the longitudinal direction is applied.
A superconducting wire of this type is, e.g., wound in a coil manner and used in practice as a large-size, high-magnetic field superconducting magnet device for nuclear fusion or for a hybrid magnet or the like. In the case of the large-size, high-magnetic field superconductor magnet device, it is demanded that the magnet device has such a structure to protect the superconducting wire itself from a strong magnetic force or to restore a superconducting state when the superconducting state is once shifted to the normal conducting state. For this purpose, a housing material made of, e.g., copper, serving as a stabilizing material and a reinforcing material is used to cover the superconducting wire body. In more detail, a housing material layer is soldered on a circumferential surface of the superconducting wire body, thereby constituting a superconducting wire.
In such a superconducting wire in which the housing material layer is soldered on the circumferential surface of the superconducting wire body, the gap between the housing material layer and the superconducting wire body is set as small as possible, e.g., about 0.1 mm or less, in order to keep good electrical contact and to improve the mechanical strength of the entire superconducting wire.
However, when the superconducting wire described above which is constituted by soldering the superconducting wire body and the housing material layer through a small gap is wound in a coil manner, although the housing material is strong against a hoop stress (which acts as a tensile stress in the longitudinal direction of a conductor) which is generated by an electromagnetic force, it has substantially no effect in reinforcement against a lateral force, as shown in FIG. 1 (this will be described later in detail as a comparative example).
Therefore, in coil design and the like, the following techniques are employed:
(a) to increase the spacer ratio; and PA1 (b) to set the height of the coil located at the innermost layer to be lower than that of the coil at the outermost layer, thereby decreasing the lateral compressive stress. PA1 a housing including at least one significant space; PA1 a superconducting wire body arranged in the housing, so as to leave the significant space in the housing; and PA1 a material filled in the significant space. PA1 a housing including at least one significant space; PA1 a superconducting wire body arranged in the housing, so as to leave the significant space in the housing; and PA1 a material filled in the significant space to leave a predetermined space. PA1 a housing including at least one significant space; PA1 a superconducting wire body arranged in the housing, so as to leave the significant space in the housing; PA1 a linear member arranged in the significant space; and PA1 a material filled in the significant space. PA1 arranging a superconducting wire body in a housing, so as to leave the significant space in the housing; and PA1 filling a material in the significant space. PA1 arranging a superconducting wire body in a housing through a significant space; and PA1 filling a material in the significant space to leave a predetermined space. PA1 arranging a superconducting wire body in a housing, so as to leave the significant space in the housing; PA1 arranging a member in the significant space; and PA1 filling a material in the significant space.
In the case of (a), however, since the stability is decreased, the reliability in terms of function is impaired. In the case of (b), since the coil design and the coil structure itself become complicated, the cost is largely increased.